This invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method for forming an image by multiple transfer using electrophotography.
Conventionally, an image forming apparatus for forming a color image by so-called electrophotography in which one of a plurality of developers supported by a rotary support member is selected by rotating them, and a latent image formed on an intermediate transfer body is developed using the selected developer is popularly used. In such image processing apparatus having an intermediate transfer body, when the surface of the intermediate transfer body is contaminated under various conditions such as the use environment, the number of prints, and the like, the density of the image formed varies, and an accurate color tone cannot be obtained.
In the conventional image processing apparatus, when the image formation environment has changed, e.g., upon power ON, exchange of a photosensitive drum, exchange of a developer, after printing a predetermined number of sheets, and so forth, density control in image formation is made to obtain an accurate color tone of a color image.
As an example of density control, a toner test image for each color density detection is formed on the intermediate transfer body, and its density is automatically detected in the apparatus. The detection result is fed back to image forming conditions such as the exposure amount, developing bias, and the like to perform density control of each color, thus allowing image formation with a stable color tone. In the density control of the conventional image processing apparatus, the formation position of the toner test image formed on the intermediate transfer body surface, the density detection timing of the toner image formed on the intermediate transfer body, and the like are controlled with reference to a detection signal obtained by an image formation start position detection sensor (to be referred to as a "TOP sensor" hereinafter) placed around the intermediate transfer body.
However, in the conventional image processing apparatus, the intermediate transfer body and a density sensor for detecting the density of a toner image formed on the intermediate transfer body are not integrated. Furthermore, since mechanical precision drops due to vibrations produced by rotation of the intermediate transfer body, it is hard to detect the toner image formed on the intermediate transfer body surface by the density sensor at an accurate timing.